The mammary gland is a complex organ which is under a myriad of regulatory controls. These include circulating hormones and growth factors, as well as local trophic factors produced by the mammary epithelial cells (MEC) or by the stroma within which the MEC are embedded. In addition, components of the extracellular matrix (ECM) exert a profound effect on both morphological and functional development of the mammary gland. During progression of MEC towards malignancy, many of these regulatory influences are lost. Considerable evidence has accumulated that stromal - epithelial interaction is altered in breast cancer, however, the time-dependent progression of the events that contribute to this change during transformation have yet to be elucidated. The long-term objective of the studies proposed herein is to determine the functional, biochemical and molecular events that comprise this altered communication between the MEC and it surrounding stroma, with the goal of developing new leads for the preVention and/or therapy of breast cancer. AIM 1. To test the hypothesis that there are alterations in stroma and/or stromal-epithelial interactions during mammary carcinogenesis, stroma will be isolated from the intact or epithelium-free ("cleared") mammary gland of rats at several times after administration of the carcinogen DMBA and the ability of isolated adipocytes and fibroblasts, evaluated separately, to induce proliferation and/or differentiation of normal, initiated and malignant MEC evaluated. The complementary possibility that normal, initiated or transformed MEC can alter stromal mitogenesis, adherence or migratory capacity will also be examined. AIM 2. It is hypothesized that growth factors or inhibitors synthesized by the stroma, or by the MEC, affect the proliferation, function, and/or differentiation of the other cell type, and that the synthesis of such modulators is progressively altered during rat mammary carcinogenesis. This will be assessed by measurement of mRNA levels by Northern blot analysis or in situ hybridization, and protein levels by Western blot analysis, immunocytochemistry, or bioactivity assays, with the main focus on TGFbeta and TNFalpha. Follow-up studies will assess the cellular consequences of this alteration in growth modulator secretion, in an attempt to assess its physiological significance and to determine whether it may play a mechanistic role during carcinogenesis. AIM 3. A second, not mutually exclusive, hypothesis that may explain an altered stromal - epithelial interaction during carcinogenesis is that the known ability of the stroma and the MEC to elaborate ECM macromolecules and/or ECM remodelling enzymes is progressively altered during carcinogenesis in such a way as to favor the growth and invasion of the transformed MEC into the mammary fat pad. To test this, the ability of stroma and MEC isolated at various times during the course of mammary carcinogenesis to synthesize and secrete ECM proteins and matrix-degrading metalloproteinases will be evaluated. Follow-up studies will assess the functional consequences of this change in cellular/ECM interaction by determining whether invasiveness, motility, adherence, or transduction of the proliferative signal is altered in the MEC or stromal cells.